The Southern Delta Aquariid Meteor Shower.

The Southern Delta Aquariid Meteor Shower is visible between roughly 12 July and 23 August each year, and is expected to peak on 30 July this year, producing up to 25 meteors per hour. Best viewing this year is predicted to be between 2.00-3.00 am (this will be in local time wherever they are viewed from, as the time reflects the orientation of the planet to the rest of the Solar System) and dawn, when the radiant point of the shower (point from which the meteors appear to radiate), which is close to the star Delta Aquari (hence the name) will be highest in the sky. This year the peak of activity will fall slightly before the first quarter moon on 1 August, and the Moon will be in the constellation of Virgo, making it reasonably distant from Delta Aqaurius in the sky, and setting before midnight, so that it should not interfere with viewing of the peak of the meteor shower.

The radiant point of the Delta Aquariid Meteors. David Dickinson/Starry Night/Universe Today.

Meteor streams are thought to come from dust shed by comets as they come close to the Sun and their icy surfaces begin to evaporate away. Although the dust is separated from the comet, it continues to orbit the Sun on roughly the same orbital path, creating a visible meteor shower when the Earth crosses that path, and flecks of dust burn in the upper atmosphere, due to friction with the atmosphere.

The Earth passing through a stream of comet dust, resulting in a meteor shower. Not to scale. Astro Bob.

The Southern Delta Aquariids are thought to be caused by the Earth passing through the trail of Comet 96P/Machholz, where it encounters thousands of tiny dust particles shed from the comet as its icy surface is melted (strictly sublimated) by the heat of the Sun. 96P/Machholz is a short period, Jupiter Family Comet, crossing our orbit every 5.24 years, but the trail of particles shed by it forms a constant flow.

How the passage of the Earth through a meteor shower creates a radiant point from which they can be observed. In The Sky.

96P/Machholz was discovered by amateur astronomer Donald Machholz from Loma Peak in California; the name 96P/Machholz implies that it was discovered by Machholz and was the 96th periodic comet discovered (a periodic comet is a comet which orbits the Sun in less than 200 years). 

The orbit and current position of Comet 96P/Machholz. JPL Small Body Database.

96P/Machholz has an orbital period of 1929 days (5.28 years) and a highly eccentric orbit tilted at an angle of 58.5° to the plain of the Solar System, that brings it from 0.12 AU from the Sun at perihelion (12% of the distance between the Earth and the Sun, considerably inside  the orbit of Mercury, and closer to the Sun than any other known periodic comet); to 5.94 AU from the Sun at aphelion (5.94 times as far from the Sun as the Earth or slightly more than the distance at which Jupiter orbits). As a comet with a period of less than 20 years, 96P/Machholz is considered to be a Jupiter Family Comet.

Image of 96P/Machholz close to the sun taken by the Solar and Heliospheric Observatory on 8 January 2002. NASA/ESA/Solar and Heliospheric Observatory.

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The Ursid Meteor Shower.

The Ursid Meteors are expected to peak at about 10 pm GMT on the evening of Sunday 22 December this year, with the shower being potentially visible to some extent between Sunday 17 and Monday 26 December.  The shower is typically best seen between midnight and dawn from anywhere in the Northern Hemisphere (it is difficult,if not impossible, to view it from the Southern Hemisphere). The extent of the shower is variable, some years producing over 100 meteors per hour at its peak, others less than 10. The peak of this years shower coicides with the Third Quarter Moon, also on 22 December, so viewing may be somewhat impaired, as glare from the Moon can hinder the viewing of meteors. The meteor shower gets its name from the constellation of Ursa Minor, in which it appears to originate.

The radiant (apparent point of origin) of the Ursid Meteors. BBC Science Focus Magazine/PA.

Meteor streams are thought to come from dust shed by comets as they come close to the Sun and their icy surfaces begin to evaporate away. Although the dust is separated from the comet, it continues to orbit the Sun on roughly the same orbital path, creating a visible meteor shower when the Earth crosses that path, and flecks of dust burn in the upper atmosphere, due to friction with the atmosphere.

The Earth passing through a stream of comet dust, resulting in a meteor shower. Not to scale. Astro Bob.

The Ursid Meteor Shower is caused by the Earth passing through the tail of Comet 8P/Tuttle, and encountering dust from the tail of this comet. The dust particles strike the atmosphere at speeds of over 200 000 km per hour, burning up in the upper atmosphere and producing a light show in the process. The Earth does not need to pass close to Comet 8P/Tuttle for the meteor shower to occur, it simply passes through a trail of dust from the comet's tail that is following the same orbital path. Comet 8P/Tuttle visits the Inner Solar System once every 13.6 years, last doing so in 2021.

How the passage of the Earth through a meteor shower creates a radiant point from which they can be observed. In The Sky.

Comet 8P/Tuttle was discovered by Horace Parnell Tuttle on 5 January 1858. The designation 8P/Tuttle indicates that it was the eighth comet discovered (people have known about comets for thousands of years, but it was only realised that they were objects orbiting the Sun, which could be repeatedly observed and predicted, in the mid-eighteenth century), that it is a Periodic Comet (comet with an orbital period of less than 200 years) and that it was discovered by Horace Parnell Tuttle.

Comet 8P/Tuttle imaged from Weißenkirchen in der Wachau in Austria on 30 December 2007. Michael Jäger/Spaceweather.

Comet 8P/Tuttle has an orbital period of 4972 days (13.6 years) and a highly eccentric orbit tilted at an angle of 55.0° to the plain of the Solar System, that brings it from 1.03 AU from the Sun at closest perihelion (103% of the distance between the Earth and the Sun) to 10.4 AU from the Sun at aphelion (10.4 times as far from the Sun as the Earth or slightly outside the orbit of the planet Saturn). As a comet with a period of less than 20 years, 8P/Tuttle is considered to be a Jupiter Family Comet.

The calculated orbit and position on 21 December 2024 of 8P/Tuttle.  JPL Small Body Database.

This means that 8P/Tuttle has occasional close encounters with the Earth, with the last thought to have happened in January 2008 and the next predicted in December 2048. The comet also has occasional close encounters with the planets Jupiter, which it last came close to in December 1995 and is next predicted to pass in September 2078, and Saturn, which it last came close to in February 1930 and is expected to pass again in February 2107. Objects which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet. 

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The Southern Delta Aquariid Meteor Shower.

The Southern Delta Aquariid Meteor Shower is visible between roughly 12 July and 23 August each year, and is expected to peak on Tuesday 30 July this year, producing up to 25 meteors per hour. Best viewing this year is predicted to be between 3.00 am (this will be in local time wherever they are viewed from, as the time reflects the orientation of the planet to the rest of the Solar System) and dawn, when the radiant point of the shower (point from which the meteors appear to radiate), which is close to the star Delta Aquarii (hence the name) will be highest in the sky. This year the peak of activity will fall a few days before the new moon on 4 August, and the Moon will be in the constellation of Taurus, rising slightly after midnight on 30 July, so light interference should be minimal.

The radiant point of the Southern Delta Aquariid Meteor Shower. EarthSky.

Meteor streams are thought to come from dust shed by comets as they come close to the Sun and their icy surfaces begin to evaporate away. Although the dust is separated from the comet, it continues to orbit the Sun on roughly the same orbital path, creating a visible meteor shower when the Earth crosses that path, and flecks of dust burn in the upper atmosphere, due to friction with the atmosphere.

The Earth passing through a stream of comet dust, resulting in a meteor shower. Not to scale. Astro Bob.

The Southern Delta Aquariids are thought to be caused by the Earth passing through the trail of Comet 96P/Machholz 1, where it encounters thousands of tiny dust particles shed from the comet as its icy surface is melted (strictly sublimated) by the heat of the Sun. 96P/Machholz is a short period, Jupiter Family Comet, crossing our orbit every 5.24 years, but the trail of particles shed by it forms a constant flow.

How the passage of the Earth through a meteor shower creates a radiant point from which they can be observed. In The Sky.

96P/Machholz 1 was discovered by amateur astronomer Donald Machholz from Loma Peak in California on 12 May 1996. The name 96P/Machholz implies that it was the first comet discovered by Machholz and was the 96th periodic comet discovered (a periodic comet is a comet which orbits the Sun in less than 200 years). 

Comet 96P/Machholz 1 imaged on 4 April 2007 by the SECCHI inner Heliospheric Imager on the STEREO Ahead space-based observatory. NASA/Wikimedia Commons.

96P/Machholz1 has an orbital period of 1931 days (5.29 years) and a highly eccentric orbit tilted at an angle of 58.1° to the plain of the Solar System, that brings it from 0.12 AU from the Sun at perihelion (12% of the distance between the Earth and the Sun, considerably inside  the orbit of Mercury, and closer to the Sun than any other known periodic comet); to 5.95 AU from the Sun at aphelion (5.96 times as far from the Sun as the Earth or slightly more than the distance at which Jupiter orbits). As a comet with a period of less than 20 years, 96P/Machholz 1 is considered to be a Jupiter Family Comet.

The orbit and position of 96P/Machholz 1 on 30 July 2024. JPL Small Body Database.

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Possible new meteor showe to be visible from North and West Australia, Papua New Guinea, New Zealand, and Indonesia, on 12 December 2023.

Comet 46P/Wirtanen was discovered in January 1948 by Carl Wirtanen, an astronomer at the Lick Observatory in the Diablo Range just east of San Jose, California. It is a Jupiter Family Comet (i.e. a comet with a period of less than 20 years), with an orbital period of 1987 days (5.44 years) and an estimated nucleus diameter of 1.2-1.4 km. The surface of the comet is considered to be 'hyper-active', meaning that its active surface area is higher than expected. 46P/Wirtanen was the initial intended target of the Rosetta space probe, with the mission being redirected to Comet 67P/Churyumov-Gerasimenko after a launch delay. The comet has periodic close encounters with both Earth and Jupiter, with the most recent close encounter with Jupiter being in 1972 and the most recent close encounter with Earth being in 2018.

Comet P46/Wirtanen crossing a dark, moonless night sky on 17 December 2023, with the Pleiades Cluster in the background. University of Arizona.

As a Near Earth Comet, P46/Wirtanen has the potential to be the source of meteor showers. Furthermore, an optical trail (i.e. a trail of debris derived from the comet, which had remained coherent some time after the comet's passage) associated with the comet was observed in 2019, although no observed meteor shower has ever been connected to P46/Wirtanen.

In a paper posted on the arXiv database at Cornell University on 6 December 2023, and accepted for publication in the journal Astronomy & Astrophysics, Jérémie Vaubaillon of the Observatoire de Paris at Université Paris Science & Letters, Sorbonne Université, and the Université de Lille, Quanzhi Ye of the Department of Astronomy at the University of Maryland, and the Center for Space Physics at Boston University, Auriane Egal, also of the Observatoire de Paris, Université Paris Science & Letters, Sorbonne Université, and the Université de Lille, and of the Planétarium de Montréal, and the Department of Physics and Astronomy at the University of Western Ontario, Mikiya Sato of the National Astronomical Observatory of Japan, and Danielle Moser of the NASA Meteoroid Environment Office at Marshall Space Flight Center, revisit the possibility of a meteor shower being caused by Comet 46P/Wirtanen, and propose a possible event in December 2023.

The orbit and curent position of Comet 46P/Wirtanen. JPL Small Body Database.

Simulations of the orbit of 46P/Wirtanen show that periodic encounters with Jupiter will change its orbit, hampering modelling of the comet's behaviour too far into the past. However, the cumulative effect of these is quite minimal as far back as 1830, enabling a reasonable level of prediction over the past 200 years.

Time-evolution of the nominal (black), average (red) and median (green) orbital elements of 1000 clones of comet 46P/Wirtanen generated in 2018. The blue curve represents the one standard deviation range about the average orbital element. All comet clones follow a similar evolution until 1830. Vaubaillon et al. (2023).

The passage of meteoroid streams generated by comets is notoriously difficult to predict. Vaubaillon et al.'s models show that the trail left by 46P/Wirtanen has intersected the Earth previously, although the density of the dust during these encounters is uncertain. Dust trails left by the comet between 1925 and 1950 were shown to have intersected the Earth in 1912 and 1917, although it is likely that these trails were highly dispersed by this time, and there were no known observations of a meteor show which would have coincided with these encounters. The Earth also encountered a trail made by 46P/Wirtanen in 1974 in both 2007 and 2018, with some records made by dedicated meteor detection networks possibly relating to these encounters.

The relative trajectories of 46P/Wirtanen and the Earth mean that meteoric dust from the comet's trails will enter the Earth's atmosphere at the relatively low speed of 10.2 km per second. At this sort of speed, only millimetre-sized particles would be expected to produce a visible meteor, although radio instruments would be able to detect sub-millimetre sized meteoroids entering the atmosphere. There is precedent for such a method being used to detect meteor showers. The Arid Meteor Shower, derived from Comet 15P/Finlay, was predicted on 7 October 2021, and whilst not actually observed, was detected by the Southern Argentina Agile Meteor Radar-Orbital System and the Canadian Meteor Orbit Radar.

Encouraged by this, Vaubaillon et al. searched the database of the Canadian Meteor Orbit Radar for possible evidence of encounters with the trail of 46P/Wirtanen in 2007, 2012, 2017, and 2018, but were unable to find any conclusive signals.

The path of the 1974 trail of 46P/Wirtanen is thought to have undergone a complex evolution. In 1984 the trail would have had a close encounter with Jupiter, causing a significant change in the path of the affected meteoroids. This means that these meteoroids are no longer on the same path as the comet (which is not thought to be on a collision course with the Earth), and the Earth is likely to directly cross the trail in December 2023. However, the meteoroids are very spatially dispersed, and the Earth is not thought likely to pass through the central part of the stream, with the effect that only sub-millimetre sized particles will enter the Earth's atmosphere, while particles of up to a few centimetres in size may come within 0.05 AU of us (roughly twenty times as distant as the Moon).

Based upon their models, Vaubaillon et al. predict that the peak of meteor activity will happen between 8.00 am and 12.30 pm GMT on Tuesday 12 December 2023, although the peak of activity for larger particles (if they encounter the Earth at all), will be later, in the second half of 12 December or possibly early on 13 December. 

As with the Aid Meteor Shower, it is difficult to predict the scale of any meteor shower produced by 46P/Wirtanen. The low velocity at which the Earth will encounter the stream makes it likely that the majority of meteors will be too dim to be visible to be detectable with the naked eye, with only a tiny number of meteors (if any) being visible. However, 46P/Wirtanen is notably more active than other comets, with as much as 40% of the surface of the nucleus actively shedding material, which may lead to more meteoroids being in the trail than predicted based upon studies of other comets.

Vaubaillon et al.'s models all predict that the shower associated with 46P/Wirtanen will be best observed between 8.00 am and 12.30 pm GMT on 12 December 2023, from North and West Australia, Papua New Guinea, New Zealand, and Indonesia. The predicted radiant point of the shower is close to the star λ-Sculptoris, leading Vaubaillon et al. to propose that the meteors should be called the λ-Sculptorids. The predicted small size and low entry speeds of the meteors will make detecting them extremely difficult, nevertheless, Vaubaillon et al. strongly encourage meteor enthusiasts to perform scientific observations and send their reports to the International Meteor Organization.

Probable area of visibility of the λ-Sculptorid meteors shower. Green point represents the radiant of the shower at its peak; unshaded area is in daylight, lightly shaded area in twilight, and fully shaded area in darkness. Vaubaillon et al. (2023).

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The Southern Delta Aquariid Meteor Shower.

The Southern Delta Aquariid Meteor Shower is visible between roughly 12 July and 23 August each year, and is expected to peak on Sunday 30 July this year, producing up to 25 meteors per hour. Best viewing this year is predicted to be between 3.00 am (this will be in local time wherever they are viewed from, as the time reflects the orientation of the planet to the rest of the Solar System) and dawn, when the radiant point of the shower (point from which the meteors appear to radiate), which is close to the star Delta Aquari (hence the name) will be highest in the sky. Unfortunately, this year the Moon will be full on Tuesday 1 August, and will be in the constellation of Sagittarius, so that light interference from the Moon is likely to hamper observations of the Southern Delta Aquariid Meteors.

The radiant point of the Southern Delta Aquariid Meteor Shower. AstroGeo.

Meteor streams are thought to come from dust shed by comets as they come close to the Sun and their icy surfaces begin to evaporate away. Although the dust is separated from the comet, it continues to orbit the Sun on roughly the same orbital path, creating a visible meteor shower when the Earth crosses that path, and flecks of dust burn in the upper atmosphere, due to friction with the atmosphere.

The Earth passing through a stream of comet dust, resulting in a meteor shower. Not to scale. Astro Bob.

The Southern Delta Aquariids are thought to be caused by the Earth passing through the trail of Comet 96P/Machholz, where it encounters thousands of tiny dust particles shed from the comet as its icy surface is melted (strictly sublimated) by the heat of the Sun. 96P/Machholz is a short period, Jupiter Family Comet, crossing our orbit every 5.24 years, but the trail of particles shed by it forms a constant flow.

How the passage of the Earth through a meteor shower creates a radiant point from which they can be observed. In The Sky.

96P/Machholz was discovered by amateur astronomer Donald Machholz from Loma Peak in California; the name 96P/Machholz implies that it was discovered by Machholz and was the 96th periodic comet discovered (a periodic comet is a comet which orbits the Sun in less than 200 years). 

The orbit and current position of Comet 96P/Machholz. JPL Small Body Database.

96P/Machholz has an orbital period of 1929 days (5.28 years) and a highly eccentric orbit tilted at an angle of 58.5° to the plain of the Solar System, that brings it from 0.12 AU from the Sun at perihelion (12% of the distance between the Earth and the Sun, considerably inside  the orbit of Mercury, and closer to the Sun than any other known periodic comet); to 5.94 AU from the Sun at aphelion (5.94 times as far from the Sun as the Earth or slightly more than the distance at which Jupiter orbits). As a comet with a period of less than 20 years, 96P/Machholz is considered to be a Jupiter Family Comet.

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